Currently, most commercially available earth drills are large earth drills for large-scale projects. There are small earth drills using gasoline or diesel engines to drive vacuum pumps or using pneumatics to drive drill stems to rotate. For general small projects, the small earth drills are inconvenient to carry and occupy large construction spaces. Furthermore, their engines are noisy. Long-term operation has a great influence on the health and hearing of workers and on the residents' lives around the construction site. Complaints from the residents will affect the construction progress, and the exhaust gas will cause harm to the human body. Driven by the engines, the drill stems cannot rotate reversely, which are inconvenient to pull out after drilling the earth. Thus, additional transmission is required for reverse rotation, which increases the size and weight of the earth drill, costs and the burden of handling and operation. At the same time, the existing earth drills have no structure for passing water, the drill stems are difficult to rotate when drilling the hard rocks. Thus, the earth drills can only drill the earth in a dry manner, or are added with water-passing devices.